The invention is directed to a screening apparatus comprising at least two frame systems which are movable relative to one another, and grate bars assigned to each system. The grate bars engage in one another in pairs and are connected by means of flexible screen elements which are fastened at the latter, bridge the distance between the bars, and are tensioned and relieved of tension by means of the relative movement of the two systems caused by means of an eccentric shaft which is supported exclusively at the two systems and rotated by means of a drive.
Such a screening apparatus is described in the German Patent No. 1 206 372. In this reference, the eccentric shaft is arranged in the center of the screen length and the two systems are stabilized relative to one another by means of springs. However, this known apparatus does not meet expectations.
A vibrating screen is known from DE-A1 32 14943 in which a box, which contains at least one screen base and is flexibly supported at its ends, is connected in the area of one of its centers of oscillation with a vibration exciter. The exciter is a shaft arranged in the longitudinal center plane of the box and is provided with an unbalanced mass.
Accordingly, an irregular vibration field is created transversely as well as longitudinally, which causes an intensive loosening of the layer of material to be screened. However, this construction cannot be transferred to the screening apparatus mentioned in the beginning, in which two frames are provided which oscillate relative to one another and whose grate bars are connected with one another by means of flexible screen elements.